1. Field of the Invention
The present invention relates to portable electronic devices having a display unit for displaying images, graphics, characters, etc., and, more particularly, to a method and apparatus for displaying characters and graphics on a display unit of a portable electronic device.
2. Description of the Related Art
Liquid crystal displays (LCDs) are generally employed as display units of existing portable electronic devices. Typically, LCDs can display still images, moving images (e.g., video), computer graphic images, objects and characters (e.g., alphanumeric text).
In order to maintain portability, the size of an LCD used in a portable electronic device is typically limited. Accordingly, when the portable electronic device displays an image, a character string, or the like, which is not smaller than a predetermined size, the portable electronic device partially displays only a portion of the image, character string, or the like. After that, when an operation unit (e.g., a cross key) is operated in a predetermined direction (e.g., up, down, right, or left), the portable electronic device displays a different part of the image, character string, or the like. This display processing is called “scrolling.”
Since the LCD has a low response speed, during scrolling, a character or the like appears to leave a trail and/or flickers as it scrolls or moves across the LCD's viewable display area. This phenomenon is quite noticeable, for example, in LCDs based on Vertical Alignment (VA) and In-Plane-Switching (IPS) that have been employed for increased viewing angles used in recent years.
Accordingly, in devices incorporating a dot-scroll display, for example, previous methods of reducing the trailing and/or flickering effects during scrolling employed switching reference voltages in order to perform smoother scrolling, thereby increasing the response speed of the dot-scroll display. This method is known as the “overdrive processing method”, and is generally used to increase the response speed of the display.
In the overdrive processing method, when a data-change direction from a preceding frame to the present frame is positive (i.e., “a rise”), an applied voltage higher than usual is applied to the liquid crystal, whereas when the data-change direction from the preceding frame to the present frame is negative (i.e., “a fall”), an applied voltage lower than usual is applied to the liquid crystal, whereby a response time is shortened to provide smoother display transitions. In an LCD display unit, by using the overdrive processing method, a response speed of moving images can be increased and undesired residual images or effects that occur when moving images are displayed can be eliminated or reduced.
However, the overdrive processing method needs a large-scale and expensive driver integrated circuit (IC) or the like. Therefore, for portable electronic devices having relatively small housings, it is preferable to solve the problems of trailing and/or flickering during scrolling without providing any overdrive processing function.